1. Field of the Present Invention
The present invention relates to a ballast structure, more particularly to a ballast structure capably provided for high-intensity discharge lamp directly installed therein.
2. Description of Prior Act
A known high-intensity discharge lamp (hereinafter abbreviated as HID lamp) 80 is referred to FIG. 1. The principle to actuate the HID lamp 80 capably to emit light is briefly stated as follows. The HID lamp 80 comprises a quartz inner tube which is filled with an inert gas, e.g., Xenon. When the inert gas is ionized by a voltage as high as 23000V (or 23 kV), an electric arc is generated to produce light.
Due to discharge through ionized gas, the HID lamp 80 does not generate high heat. As long as only a few inert gases are still existed in the quartz inner tube, the HID lamp 80 can emit light constantly. Therefore, if compared with other lamps, the HID lamp 80 is less prone to damage, is capable of providing much brighter illumination over a wider angle, and has a longer service life.
However, since the gas-discharge light-emitting mechanism of the HID lamp 80 has a characteristic of negative resistance, the voltage in the HID lamp 80 does not increase but decreases as the current increases, and vice versa. If directly connected to a voltage source, the HID lamp 80 will burn once the current surges beyond its limit. In order to overcome the negative resistance of the HID lamp 80, it is required that a ballast 10 be connected in series in the circuit of the HID lamp 80, wherein the ballast 10 limits the current through the HID lamp 80 and thereby allows the HID lamp 80 to operate normally.
The HID lamp 80 can use a direct-current (DC) or alternating-current (AC) power source. As shown in FIG. 2, when a DC power source is used, the ballast 10 to be series-connected to the HID lamp 80 is connected to the DC power source by a power input cord 12 and is connected to a HID lamp seat 20 by a power output cord 14. Once the HID lamp 80 is installed on the HID lamp seat 20, the ballast 10 can convert DC power into a boosted AC power and supplies the AC power to the HID lamp 80, so as for the HID lamp 80 to emit light by gas discharge.
Conventionally, the circuit of the ballast 10 at least includes a DC boost circuit 10a, an AC rectifier circuit 10b, and an ignition circuit 10c, all of which circuits are arranged to form a circuit that provides the function of a ballast. The DC boost circuit 10a is connected to the AC rectifier circuit 10b and, as required by operation of the HID lamp 80, can boost the DC power obtained through the power input cord 12, such as a 12V DC power, to the desired voltage, which is supplied to the AC rectifier circuit 10b connected to the output end of the DC boost circuit 10a. The AC rectifier circuit 10b then converts the boosted DC power into AC power by DC/AC voltage conversion. The AC power is supplied to the ignition circuit 10c so that voltage is instantly raised to 23 kV to start and light the HID lamp 80. In addition, the AC power provides a stable AC voltage and current to the HID lamp 80 to sustain gas discharge in, and hence normal operation of, the lit HID lamp 80.
The conventional ballast 10 and HID lamp seat 20 are two independent components that are separately designed. This causes inconvenience of use, given the current design trend toward lightweight and compactness.